1. Field of the Invention
The invention relates to a suction cup suitable for hanging an object on a wall.
2. Description of the Related Art
A conventional suction cup includes an elastic cup body and a hook coupled to the cup body for hanging an object. In use, the cup body is pressed against a wall surface so that air between the cup body and the wall surface is expelled. Thereafter, when application of pressure on the cup body is ceased, the cup body tends to restore to its original shape, and a low-pressure space is formed between the cup body and the wall surface. The pressure difference between inner and outer sides of the cup body keeps the suction cup adhered to the wall surface.
However, if the elastic cup body lacks sufficient stiffness, adherence to the wall surface is weakened because the tendency of the cup body to restore to its original shape for forming the low-pressure space is weak. On the other hand, if the elastic cup body is too stiff, a good sealing effect for the low-pressure space is unlikely to be formed between the cup body and the wall surface. In both cases, adherence of the suction cup to the wall surface might not be strong enough to permit hanging of an object for long periods of time.
Another conventional suction cup includes an elastic inner cup disposed in a rigid outer cup. The outer cup is provided with a hook for hanging an object. A bolt extends threadedly into the outer cup and is coupled to the inner cup.
In use, the inner cup is placed intimately against a wall surface with a rim of the inner cup clamped tightly between the outer cup and the wall surface. The bolt is then operated to move the inner cup such that a low-pressure space is formed between the inner cup and the wall surface. Because the rim of the inner cup is clamped tightly between the outer cup and the wall surface, leakage of air into the low-pressure space may be avoided, thereby permitting hanging of an object for long periods of time. However, the need to operate the bolt when adhering such suction device on the wall surface arises in user inconvenience.